1. Technical Field
The present invention relates to a method of manufacturing a thin-film light-absorbing layer and a method of manufacturing a thin-film solar cell using the same.
2. Description of the Related Art
Materials for use in thin-film solar cells include crystalline silicon, amorphous silicon, a dye sensitizer, CIS, CIGS, CdTe, etc. Among these materials, a CIS-based compound which shows the highest theoretical efficiency is useful in the fabrication of solar cells. Currently, a CIS-based thin-film light-absorbing layer is being manufactured using a high-vacuum apparatus via co-evaporation or sputtering. As is known to date, the light conversion efficiency is about 15% at its maximum in the case of a CIS-based thin-film light-absorbing layer, and is about 20% in the case of a CIGS-based thin-film light-absorbing layer.
Although deposition of a CIS-based thin-film light-absorbing layer manufactured in a high vacuum may result in a solar cell having high efficiency, it is expensive to manufacture the light-absorbing layer, it is difficult to make one with a large area, and an expensive apparatus is needed to produce a large-area solar cell. Moreover, methods of manufacturing a light-absorbing layer from four elements such as CIGS using co-evaporation or sputtering in a vacuum are disadvantageous because an apparatus typically used therefor is high-priced, and also because the light-absorbing layer is manufactured by controlling the composition of four elements or individual binary compounds, and thus the composition is difficult to control and the manufacturing cost may increase.
Hence, research into methods of manufacturing high-efficiency thin-film solar cells not in a vacuum but in a non-vacuum where it is easier to control the composition and process, compared to CIGS-based compound solar cells typically manufactured using co-evaporation or sputtering, is ongoing. That is, in the case of thin-film solar cells manufactured using co-evaporation or sputtering in a vacuum, they have remarkably lower price competitiveness compared to fossil-fuel power cost.
Korean patent application publication No. 10-2009-0121660A discloses a method of manufacturing a CIGS thin film and a light-absorbing layer of a solar cell manufactured using the same, in which a copper precursor, an indium precursor, a gallium precursor, and a selenium precursor are mixed with water or a buffer thus preparing a mixture solution, after which voltage is applied to a potentiostat so that a CIGS thin film is electrodeposited on a working electrode. Also, a method of manufacturing a CIGS thin film in a non-vacuum is disclosed, and a CIGS thin film is manufactured using prepared particles by means of spraying thus fabricating a cell having an efficiency of 11.7% (Chris Eberspacher Chris Fredric, Karen Pauls, Jack Serra, “Thin-film CIS alloy PV materials fabricated using non-vacuum, particles-based techniques”, Thin Solid Films Vol 387, 18-22 (2001)). On the other hand, Korean patent application publication No. 10-2006-0036190A discloses a method of manufacturing an indium oxide sulfide buffer layer for a Cu(In, Ga)Se2 or Cu(In, Ga)(S, Se)2 thin-film solar cell using solution growth and a solar cell fabricated using the same, in which an indium oxyhydroxide sulfide thin film which is a new buffer material is formed to a thickness of tens of nm using an inexpensive solution growth process and a thin-film solar cell is fabricated using the same. The new buffer material used in the above patent may be grown using solution growth without post heat treatment to thus fabricate a solar cell. Also, a method of manufacturing a CIGS thin film using a CIGS solution precursor is disclosed, in which the CIGS thin film is formed from a solution precursor of CIGS using non-vacuum thin film deposition (David B. Mitzi, Min Yuan, Wei Liu, Andrew J. Kellock, S. Jay Chey, Vaughn Deline, Alex G. Schrott, “A High-Efficiency Solution-Deposited Thin-Film Photovoltaic Device” Adv. Mat., 2008, 9999, 1-6). As such, the solution precursor used may include a hydrazine solution and the CIGS thin film is formed using spin coating. In the case of a cell manufactured using a spin coated CIGS thin film, it may exhibit a light efficiency of about 12%. These methods are problematic because coating is not directly performed using the solution precursor in a non-vacuum or hydrazine which is highly toxic is used, undesirably causing environmental problems and reducing long-term stability.
Therefore, many attempts are being made to manufacture a CIS- or CIGS-based thin film in a non-vacuum in order to more easily and inexpensively fabricate a light-absorbing layer and a solar cell having a large area.